1. Field of the Invention
The present invention relates generally to an arc welding apparatus and method and more particularly to an arc welding apparatus and method which can be continuously used or employed for a long period of time so as to automatically arc weld steel substrates or the like.
2. Description of the Prior Art
In theory, it is unnecessary to have an observe welding apparatus from the beginning of the welding operation to the completion of the automatic arc welding operation; however, in an actual arc welding operation, it is usually necessary to observe and repair the welding apparatus, especially the welding torch thereof, as a result of the occurrence of undesirable phenomena, such as, for example, a consumpution of the electrode and the deposition of spatter. Accordingly, a substantial amount of labor and time have been spent in conjunction with such operations.
The present invention is contructed so as to provide welding apparatus for imparting stable welding throughout the entire welding operation without the necessity of repairing the welding torch. The disadvantages of conventional arc welding methods will be apparent from FIG. 1 which is a schematic view of a torch of a conventional carbon arc are welding apparatus wherein, in accordance with well-known welding methods, economical carbon dioxide gas or a mixture of carbon dioxide gas and oxygen is utilized as a shielding gas. (Hereinafter, carbon dioxide gas and a mixture of carbon dioxide gas and oxygen are referred to simply as carbon dioxide gas.)
Within FIG. 1, power is supplied to a welding flux rod 1 through means of a contact chip 2 so as to ignite an arc 4 between the rod and a substrate or base metal 3 and to form a pool of melted metal 5. In order to prevent permeation of atmospheric nitrogen into the molten pool 5, a shielding gas 7 is fed from a shielding nozzle 6 so as to protect the molten pool 5. Within such a carbon dioxide arc welding method, economical carbon dioxide gas is used as the shielding gas and the welding rod 1 contains a large amount of silicon (Si) and manganese (Mn) as a deoxidizing agent for removing oxygen contained within the molten pool 5.
Accordingly, within the welding process, the reaction of the deoxidizing agent such as, for example, silicon and manganese, with the oxygen of the steel substrate or base metal is performed within the pool of melted metal so as to result in the formation of slag of SiO.sub.2, MnO and the like which floats upon the pool of melted metal. The remaining deoxidizing agent which does not react with the oxygen of the steel substrate reacts with the oxygen produced by means of dissociation from the carbon dioxide and such also floats as a slag, this being a fundamental principle of carbon dioxide arc welding methods.
Within the welding operation, a large amount of spatter is also formed, as shown in FIG. 2, a part of the melted metal 8 at the end of the welding rod being scattered out of the arc 4 in the form of fine drops 9 without travelling to the base metal 3, as shown within FIG. 2a, and such is also deposited upon the end of the contact chip 2, as well as upon the end of the shielding nozzle 6 of FIG. 1, so as to prevent the welding operation from continuing. In addition, in the case of travelling with contact as shown in FIG. 2b, the melted metal 8 is scattered out of the arc 4 in the form of fine drops 9 by tearing away the melted metal at the decontacting step, and a similar phenomenon is found in the case of the discharge of gas from the pool of melted metal 5.
In all cases, the scattered fine drops 9 or spatter are deposited upon the end of the nozzle and upon the bead, which of course deteriorates the appearance of the latter, and the flow of the shielding gas 7 is disturbed so as to impart inferior welding results. In severe cases, the feed of the welding rod 1 is stopped. Accordingly, it is necessary to clean around the contact chip during the welding operation and consequently, continuous operation has not been achieved.
FIG. 3 shows a torch used within a conventional T I G welding operation wherein a non-consumable electrode 10 having a high melting point, such as, for example, tungsten, is used as the electrode and the arc 4 is ignited between the electrode and the base metal or substrate 3. During the operation, an inert gas 7, such as, for example, argon, is fed from within the shielding nozzle 6 as a shielding gas in order to protect the molten pool 5 from the atmosphere, and the welding can also be carried out by inserting a welding rod between the electrode 10 and the substrate 3.
Within such method, however, the electrode 10 is not protected whereby the end of the electrode 10 is polluted by means of the spatter of the molten pool 5, the metal vapor, and the scatter of fine drops of the welding rod during a long continuous operation. Accordingly, it is necessary to grind the end of the electrode with a grinder. If the grinding operation is neglected, a stable arc cannot be maintained and the consumption of the electrode is accelerated. Accordingly, it is necessary to closely observe the condition of the end of the electrode, and therefore continuous operation has been difficult.
It is additionally noted that the arc 4 is surrounded by the shielding gas 7 but is not guided thereby and consequently the arc is not restricted or constricted so as to be maintained the same in the direction of the electrode, the arc 4 therefore being somewhat movable, whereby a tortuous bead has been formed. These phenomena have been easily caused by pollution of the electrode 10 and it is necessary to control the welding condition from this viewpoint. Still further, when the composition of the steel contains large amounts of gaseous components, a large amount of gas has been discharged from the molten pool 5 upon solidification so as to form or produce welding defects 11, such as, for example, blow holes within the welded part.